If you've been in Arizona for any length of time, you usually know when it's going to rain. No, not the towering brown wall of dirt on the horizon. That's usually just a tease.

We're talking about the smell, the scent. Rain in the desert possesses a distinct aroma. To many of us, it smells like home.

That magical fragrance comes courtesy of larrea tridenta, or the creosote plant, which grows only in the arid Southwest areas of United States and Mexico, including the Mojave, Sonoran and Chihuahuan deserts. The oils of plant become active in rain, perfuming the air with that tell-tale eau de desert.

“The creosote bush is a remarkable plant,” Boyce Thompson Arboretum naturalist Terry Stone says. “The resinous nature of the plant leaves explain why they are so aromatic when it rains.”

But don't confuse the creosote bush with creosote oil, a coal-tar petroleum product used to preserve wood crates, palates and telephone poles. The oils smell nothing alike. One conjures hikes at South Mountain, the other of an industrial shipyard.

Other names, uses

The resins of the creosote bush have also led to it being called greasewood. There's the towns of Greasewood and Greasewood Springs in northern Arizona, and, of course, the old Greasewood Flats restaurant in Scottsdale.

“Some people also call it chaparral,” Stone says. “Just understand that these are regional names that are also applied to other plants.”

Indigenous people have known of creosote's virtues for centuries, mostly as a medicinal herb, Stone says.

“Poultices, teas, etc. was how it was used,” he says. “Kind of a 'cure all.'

“But my understanding is that too much of it can be hard on the liver and kidneys. And, having had some creosote tea, I can attest to how bitter it is.”

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It can't be any worse than some of those medicinals teas at health food stores like nettle or dandelion leaf. I don't care how “good” it is for you, the stuff tastes nasty.

Long life

Stone also says that creosote bushes live a long time, like thousands of years. He says a plant grows a “root crown” that sprouts a few limbs. Then the limbs grow leaves and produce flowers, then seeds.

“After a few years, those limbs will die, but, from the same root crown, on its expanding outer edge, more limbs sprout and grow,” Stone says. “Then they die, but the same root crown will produce more limbs” creating a ring of new growth.

“(Creosote) can have one of the longest lives of any living organism on Earth,” Stone says.

He cites one specimen in California's Lucerne Valley called “King Clone” that's thought to be 12,000 years old.

Think about that the next time it rains and that wonderful scent wafts over you.